The present invention generally relates to a method and apparatus for making a mechanical fastener. The present invention relates more particularly to a method of making a mechanical fastener which includes heating stem ends to form softened ends and thereafter deforming the softened ends into convex heads with a deformable surface. The present invention also relates more particularly to an apparatus for making a mechanical fastener which includes a web conveyor, a heating source located adjacent the web conveyor, and a deformable surface located down the web from the heating source.
Various types of mechanical fasteners are known for holding articles together, such as hook and loop type fasteners or complementary pairs of fasteners that engage with one another. The complementary pairs of fasteners typically have engaging surfaces with patterns of stems having heads. Various methods have been used to head the stems of these fasteners. For example, U.S. Pat. No. 5,077,870, xe2x80x9cMushroom-Type Hook Strip for a Mechanical Fastener,xe2x80x9d (Melbye et al.), describes a method for forming mushrooms on an array of upstanding stems. A web having an array of upstanding stems made of thermoplastic resin is fed between two calendar rolls. The roll that contacts the stems heats the tips of the stems to a temperature exceeding the flow point of the thermoplastic resin. Briefly, Melbye et al. states that maintaining the tips at this temperature allows molecular disorientation to take place. During this time and upon subsequent cooling, the tips draw back to form uniformly shaped mushroom heads, each having an upper, substantially convex surface and a larger cross section than the original stem.
PCT publication WO 98/57564, xe2x80x9cMethod and Apparatus for Forming Headed Stem Mechanical Fastener Structure, (Kampfer), published on Dec. 23, 1998, describes a method of deforming the hook head portions of hook elements on a web backing. The hook elements on the web backing are fed into a nip formed between a support surface and an upper heated surface having a durometer hardness of less than 90 Shore A. This upper heated surface compressively engages the hook head causing it to turn down and permanently deform. This increases the uniformity of the hook head elements forming a fiber engaging crook region.
U.S. Pat. No. 5,505,747, xe2x80x9cMethod of Making an Abrasive Article,xe2x80x9d (Chesley et al.), describes a method for making an abrasive article, including the steps of providing a substrate having abrasive means on one surface, and providing a plurality of hooking stems on the opposite surface thereof. In one preferred embodiment, Chesley et al. describes a method of providing hooking means, in the form of a head adjoining each stem, by heating the stems with a heated plate to thereby deform the distal end of the stem, but may also be provided by contacting the distal ends of the stems with a heated calendering roller to form the heads.
U.S. Pat. No. 3,192,589, xe2x80x9cSeparable Fastener,xe2x80x9d (Pearson), describes a method of making a fastener including a plurality of headed studs in a flexible base. In one embodiment, Pearson describes a method of making a fastener that includes two operations. The first step is molding the base integrally with the studs in headless form. The stud lengths have to be such that they contain enough material to form the required size heads for the selected design and should also be tapered enough to facilitate ejection of the unit from the mold. The second operation involves heat softening and upsetting the tips of the studs, such as in a heading die. The heading operation is a relatively slow squeezing action rather than an impact. The die needs to shape the heads only from the top and sides because the combined heat and squeeze action gives an effective rolling upset to the heads.
U.S. Pat. No. 3,527,629, xe2x80x9cMethod of Producing Fastener Member having Upstanding Fastener Elements Shaped for Releasable Engagement with Cooperating Fastener Elements,xe2x80x9d (Wylde), describes a method of making a fastener member including a strip of plastic sheet material and a large number of filamentary fastener means each in the form of generally U-shaped metallic wire. In one preferred embodiment, Wylde describes a method of deforming straight upstanding limbs so that they are capable of releasable engagement with like or cooperating elements on another fastener member. The limbs are received in a slot in an anvil which is moved in a direction parallel to the surface of the strip to the position on either side of the limb. The free end of the limb projects above the anvil and is acted on by a downward movement of a former provided with a generally cup shaped recess. The recess is shaped to bend the end of the limb downwardly onto a tapered side of the anvil.
Co-pending U.S. patent application Ser. No. 09/290,751, filed on Apr. 13, 1999, xe2x80x9cA Mechanical Fastener and Method for the Same,xe2x80x9d (Aamodt et al.) discloses a method of making a mechanical fastener that includes placing a layer of heated material on stem ends to soften the stem ends and deforming the softened stem ends into convex heads. In one preferred embodiment, prior to the substrate entering a nip formed between a first and second roller, a layer of heated material is extruded from an extruder onto the tips of the stems. The layer of material is at a temperature high enough to soften the ends of the stems. Heads are then formed on the stems by deforming the softened ends into heads as the substrate, stems and layer of material pass through the nip.
The present invention provides a method and apparatus for forming a mechanical fastener. One aspect of the present invention provides a method of forming a mechanical fastener. The method of forming a mechanical fastener comprises the steps of: a) moving a substrate along a web path, where the substrate includes a first major surface and a plurality of stems extending from the first major surface of the substrate, and where each of the stems includes a stem end; b) radiantly heating the stem ends to form softened ends; and c) thereafter deforming the softened ends into convex heads with a deformable surface.
In one preferred embodiment of the above method, step c) includes compressing the softened ends with an elastic surface. In another preferred embodiment of the above method, the temperature of the deformable surface is less than the temperature of the softened ends. In another preferred embodiment of the above method, step b) includes heating the stem ends to form molten ends.
In another preferred embodiment of the above method, step c) includes compressing the substrate between a nip formed between a first roller and a second roller, where the second roller includes the deformable surface, where the first roller contacts the substrate opposite the first major surface, and where the second roller contacts the softened ends. In another aspect of this embodiment, the temperature of the deformable surface of the second roller is less than the temperature of the softened ends. In another aspect of this embodiment, the temperature of the deformable surface of the second roller is less than 270xc2x0 F. In yet another aspect of this embodiment, the deformable surface of the second roller is between 40xc2x0 F. and 185xc2x0 F. In another aspect of this embodiment, the deformable surface of the second roller is elastic. In yet another aspect of this embodiment, the deformable surface of the second roller has a durometer hardness between. 10 Shore OO and 70 Shore A. In yet another aspect of this embodiment, the deformable surface of the second roller has a durometer hardness of between 10 Shore OO and 20 Shore OO. In another aspect of this embodiment, the deformable surface of the second roller has a roughness measurement (Ra) of less than 30 micro-inch. In another aspect of this embodiment, the deformable surface of the second roller has a roughness measurement (Ra) of less than 20 micro-inch.
In another preferred embodiment of the above method, step b) includes heating the stem ends to a temperature above 270xc2x0 F. In another aspect of this embodiment, step b) includes heating the stem ends to a temperature between 270xc2x0 F. and 600xc2x0 F. In another preferred embodiment of the above method, the elastic surface has a durometer hardness of less than 70 Shore A. In yet another preferred embodiment of the above method, the elastic surface has a durometer hardness of between 10 Shore OO and 20 Shore OO. In another preferred embodiment of the above method, step b) includes heating the stem ends with an infrared heat source.
In yet another preferred embodiment of the above method, the substrate and the plurality of stems comprise a polymeric material. In another aspect of this embodiment, the polymeric material comprises a thermoplastic material. In another aspect of this embodiment, the thermoplastic material comprises a polyolefin. In yet another aspect of this embodiment, the polyolefin comprises polypropylene.
Another aspect of the present invention provides a mechanical fastener made by any of the methods described above.
Another aspect of the present invention provides an alternative method of forming a mechanical fastener. The method of forming a mechanical fastener, comprises the steps of: a) moving a substrate along a web path, wherein the substrate includes a first major surface and a plurality of stems extending from the first major surface of the substrate, wherein each of the stems includes a stem end; b) radiantly heating the stem ends to form softened ends; and c) thereafter deforming the softened ends into convex heads with a deformable elastic surface, wherein the deformable surface has a durometer hardness of between 10 Shore OO and 70 Shore A, where the deformable surface has a roughness measurement (Ra) between 5 micro-inch and 30 micro-inch, and where the temperature of the deformable surface is less than the temperature of the softened ends.
Another aspect of the present invention provides an apparatus for forming a mechanical fastener. The apparatus for forming a mechanical fastener, comprises: a) a means for moving a substrate along a web path, where the substrate includes a first major surface and a plurality of stems extending from the first major surface of the substrate, and where each of the stems includes a stem end; b) a means for heating the stem ends to form softened ends; and c) a means located down the web path for deforming the softened ends into convex heads, where the means for deforming includes a deformable surface having a durometer hardness between 10 Shore OO and 70 Shore A.
In one preferred embodiment of the above apparatus, the deformable surface is elastic. In another preferred embodiment of the above apparatus, the deformable surface has a durometer hardness of between 10 Shore OO and 20 Shore OO. In yet another preferred embodiment of the above apparatus, the deformable surface has a surface roughness (Ra) of less than 30 micro-inch.
Another aspect of the present invention provides an alternative apparatus for forming a mechanical fastener. The apparatus for forming a mechanical fastener, comprises: a) a web conveyor, where the web conveyor defines a web path; b) a heating source located adjacent the web conveyor; and c) a deformable surface located down the web path from the heating source, and where the deformable surface has a durometer hardness between 10 Shore OO and 70 Shore A.
In one preferred embodiment of the above apparatus, the deformable surface is elastic. In another preferred embodiment of the above apparatus, the deformable surface has a durometer hardness of between 10 and 20 Shore OO. In another preferred embodiment of the above apparatus, the deformable surface has a surface roughness (Ra) of less than 30 micro-inch.